Isomerization of butene-1 to cis-butene-2

ABSTRACT

Butene-1 is isomerized principally to cis-butene-2 by contacting butene-1 in liquid phase with a molecular sieve having an effective pore size of greater than 5 and less than 10 A. at e.g. 100*C. Prior to use the molecular sieve was activated at a temperature of 400*-450*C. in a stream of nitrogen and 3 percent oxygen. Conversion to butene-2 was 32 mole percent of which 51.3 percent was the cis form. The cis-butene-2 is a useful feed for oxidative dehydrogenation to butadiene.

[ Mar. 27, 1973 ISOMERIZATION OF BUTENE-l TO CIS-BUTENE-2 [75'] I Inventors: Calvin M. Tidwell; Val G. Henne'berg, both of Houston, Tex.

[73] Assignee: Petro-Tex Chemical Corporation,

Houston, Tex.

22 Filed: Nov. 24, 1969 [21] Appl.No.: 879,581

UNITED STATES PATENTS 10/1969 Manning ..260/683.2.

9/1969 Kahn ..'260/683.2 11/1968 Mitsche ..260/683.2

Primary ExaminerDelbert E. Gantz Assistant ExaminerVeronica OKeefe Attorney-G. Baxter Dunaway ABSTRACT Butene-l is isomerized principally to cis-butene-2 by contacting butene-l in liquid phase with a molecular sieve having an effective pore size of greater than 5 and less than 10 A. at e.g. 100C. Prior to use the molecular sieve was activated at a temperature of 4OQ450C. in a stream of nitrogen and 3 percent oxygen. Conversion to butene-2 was 32 mole percent of which 51.3 percent was the cis form. The cis-butene-2 is a useful feed for oxidative dehydrogenation to butadiene.

10 Claims, No Drawings ISOMERIZATION OF BUTENE-l T CIS-BU'IENE- "2 The present invention relates to a process of isomerization of butene-l to butene-2 using a pretreated molecular sieve catalyst. Butene-2 is the preferred feed for the preparation of butadiene, particularly butadiene-l,3, by oxidative dehydrogenation, for example, as shown in the US. Pat. Nos. 3,260,767; 3,274,285; 3,284,536; 3,303,234-7 and 3,320,329. A great deal of investigation has been carried out on isomerization of butene-l over various catalysts including some investigations in regard to molecular sieves. However, past efforts using molecular sieves have been generally disappointing, producing conversions of less than 5. percent to butene- 2. According to the present invention much higher conversions are achieved. Another salient feature of the present isomerization is the production of a predominate amount of the cis-butene-2. In the majority of processes for the isomerization of butene-l to butene-2, the trans isomer is the predominant isomer formed.

Cis-butene-Z is a useful feed for oxidative dehydrogenation and has been observed to be somewhat more active therein than the trans form.

Briefly stated, thepresent invention is a process for isomerizing butene-l to butene-2 comprising contactskeleton is composed of silicon and aluminum atoms each surrounded by four oxygen atoms to form a small pyramid -of tetrahedron (tetrahedral coordination).

The term molecular sieve can be appl-ied'toboth naturally occurring zeolites and synthetic zeolites. Naturally occurring zeolites have irregular pore size and are not generally considered as equivalent to synthetic zeolites. In the present invention, however, naturally occurring zeolites are acceptable so long as they are substantially pure and have substantially all of their pores of greater than about 5 and less than about Angstroms size. The balance of the present discussion shall be directed to the synthetic zeolites with the understanding that natural zeolites are considered equivalent thereto as indicated above, i.e., in so far as the natural zeolites are the functional equivalents of the synthetic zeolites.

Usually synthetic zeolites are prepared in the sodium form', that is, with a sodium cation in close proximity to each aluminum tetrahedron andbalancing its charge. To date four principal types of molecular sieves have been reported, A, X, Y, and L. The A type have relatively small pore size. By the term pore size is meant the effective pore size (diameter) rather than the free pore size (diameter). Type 5A having an effective pore size of approximately 5 A (free diameter 4.2'A) has not been found suitable for the present process. Types X and Y have larger pore size (up to approximately 10 A) and differ as to the range of ratio of A 10 to SiO as:

Type X NaO "A1 0 2.0-3.0 Si0 Type Y NaO -AI O 3.0-6.0 Si0 Type L has still higher ratios of SiO to A1 0 The pore size within thecrystal lattice is important to the present reaction. According to one theory of molecular sieve catalytic activity, zeolite catalysis occurs primarily inside the uniform crystal cavities, consequently zeolitic catalyst activity depends on the number of aluminum atoms in the crystal and thus on the chemical composition of the crystal. Moreover, these catalytic sites are fixed within the rigid structure of the crystal, so that access to sites can be altered by altering the structure of the crystal. It has been found that molecular sieves suitable for the present invention must have an effective pore size of greater than about 5 A and less than about 10 A, prefereably a molecular sieve having an effective pore size of about 8 A is employed and more preferably an'X type. The effective pore size reflects the size of the molecules that can pass through'the sieve. It has been observed that the elasticity and kinetic energy of the incoming molecules,

generally, allows easy passage of molecules up to 0.5

Angstroms larger than the free diameter of the aperature.

The molecular sieve employed according to this invention is activated by heating the molecular sieve at a temperature at least 300C. and more preferably at about 320 500C. Generally the heating is continued for A to 5 hours. The heating can-be carried out in air or other non-reactive gases such as nitrogen, helium, argon or various mixtures thereof. Preferably there is someoxygen present in the non-reactive gas. In a similar manner a a used catalyst can be regenerated by found that in the regenerations the molecular sieve mustbe heated to, at least 400C. If not, there is no regeneration and activation. Thus, the regeneration and activation temperature of 400 600C. is critical. One means of controlling the temperature during the regeneration activation is to maintain control over the oxygen that is used to burn off the accumulated residue on the catalyst. This is quite simply done by maintaining a small volume, e.g., 1 10 percent oxygen in the stream of non-reactive gas. The term non-reactive gas is used here to indicate a gas that does not react with, or react in regard to the molecular sieve, i.e., does not use up the catalyst. In this sense then oxygen, which reacts to burn off any accumulated residue on the catalyst is non-reactive.

The isomerization reaction will proceed at relatively low temperatures, i.e., around 25C. but it has been found that the yield-of butene-2 is increased by using elevated temperatures for example 50 to C. The reaction is conducted in liquid phase and the pressure is adjusted to maintain the reactants in a substantially liquid condition. This will generally require pressures of greater than 1 atmosphere to 50 or more atmospheres. The rate of feed to the reactor can vary over a wide range but will generally have a liquid hourly space velocity (LI-ISV) of from 5 to 15 (stated as reciprocal hours).

' also undergo various reactions such as isomerization,

disproportionation, polymerization, etc. A particularly 7 useful feed would be one comprising 40 to 60 mole percent butene-l 6 to mole percent n-butane, 0 to 4 mole percent isobutylene, and 30 to 50 mole percent butene-2. In a preferred embodiment of this invention the quantity of butadiene is limited to less than 3 percent preferably 0 3 percent. Although butadiene does 1 not have any effect on the isomerization it does have a tendency to polymerize on the molecular sieve, thus, clogging the pores and limiting the throughput between regenerations.

When the isomerization is practiced according to this invention the yield of butene-2 is substantially in creased, i.e., 2 and 3 times the yield without prior activation of the molecular sieve catalyst. Two forms of butene-Z are possible, the transand the cis. Surprisingly, the present isomerization yields predominately the more active cis form whereas prior isomerizations yielded principally 'the trans form. The term predominately" is used herein and in the claims to indicate an amount over ,50 percent. Unless otherwise specified the percentages used herein are mole percents. The following examples will further illustrate the invention. Identification of feed and product constituents are made by gas liquid chromatography.

, EXAMPLE,

The reactions described below were carried out in an apparatus which had a feed system comprising a reservoir and a calibrated variable stroke positive displacement pump connected to the reactor system. The reactor system consisted of two jacketed stainless steel reactors each containing a pressure relief valve set at 300 p.s.i.g. to maintain the feed streams in liquid phase.

Reactor 1 had an internal volume of 67 ml. and could be operated at temperatures up to 115C. Reactor 2 had an internal volume of 500 ml. ln operation, it was filled with 200 ml. of 4 8 mesh quartz chips, followed by 300 ml. of the test molecular sieve. Reactor 2 was equipped with electrical heaters and could be operated at'temperatures up to 450C. It was also equipped with a by-pass valving system and flow meters so that it could be regenerated with air-nitrogen mixtures and such as n-butane. The reactors were connected to an effluent system comprising an expansion section where the effluentwas vaporized and brought to ambient temperature (about 25 C.), a knock-out pot to collect any non-volatile products, and a wet test meter to measure the effluent gas volume. The off gas was analyzed at frequent intervals and the effluent volumes calculated. The results of the analyses of feed and product are shown in the Table.

Run 1. Reactor 1 was charged with Type 5A molecular sieve (effective pore size less than 5 A, i.e., about 4.7 A) which had been activated in air at'320C. The run was carried out at room temperature about 25 C.) and 12.0 LHSV.

Run 2. Reactor 1 was charged with 10X molecular sieve(effective pore size of about 8 A) which was pretreated in air at 320C. and run at about 25C., LHSV 12.0.

Run 3. Same as Run 2 but run at 100 LH'SV 12.0

Run 4.- Reactor 1 was charged with Type 13X molecular sieve (effective pore size about 10 A) which was pretreated-at 320 C. in air and run at 100 C., and

LHSV 12.0.

0 Run 5. Reactor 2 was charged with Type 10X molecular sieve which had been activated at 320C. in air. The reactor was preloaded with liquid n-butane and the run carried out at 100C. at LHSV of 6.4.

Run The charge of run 5 was regenerated in situ at 400 450C. for 3 hours in a stream of 3 percent oxyg'en in nitrogen and cooled to room temperature (about 25 'C.) in nitrogen only and preloaded and run as in Run 5.

Run 7. The charge of Run 6 was exhausted and Feed-Product Volume. ml. Liquid isomerization of Butene- 1% R trans cis to trans to cis No. n-Butane Butene-l Butene-2 Butene-2 Butadiene 'lsobutylene Heavy Oils Butane-2 Butene-2 I Feed 88 446 269 18 6 2 Product 439 278 20 5 2 0 Net change 3 7 9 2 1 I 0 0 79.5 20.5 2 Feed 89 452 272 18 6 2 Product 85 429 254 40 1 0 29 Net change 4 23 18 22 5 2 29 95.7 3 Feed 459 2338 1408 92 29 11 Product 451 2185 1354 289 6 2 63 Net change 8 153 54 +197 23 9 63 128.8 4 Feed 103 567 301 19 7 3 Product 103 566 303 19 7 3 0 Net change 0 1 2 o 0 0 0 0 0 5 Feed 6428 2571 97 21 343 0 Product 5751 2695 561 0 34 174 Net change 677 124 464 21 309 74 18.4 68.6 6 Feed 5477 2191 83 18 292 Product 3734 2538 978 '0 25 547 Net change 1743 347 895 18 267 547 19.9 51.3 7 Feed 10955 4381 1.65 36 584 0 Product 8534 4955 1705 l 42 414 Net change 2421 574 1540 35 542 414 23.7 63.6

vapor or liquid preloaded with an inert hydrocarbon FOOTNOTES FOR TABLE are based on Butenel net change, thus, in Run 3 there is an apparent yield of cis-butene-2 of 428.8, actually some trans-butene-Z or other monomer must also be undergoing isomerization to cis-butene-2. "Since the molecular sieve was preloaded with n-butane in runs 5 7 no point could be served in reporting n-butane in the feed and product streams, in any event n-butane appears to be essentially inert in the present reactions.

The invention claimed is:

l. A process for isomerizing butene-l to butene-2 comprising contacting a feed containing butene-l in liquid phase at a liquidhourly space velocity of from 5 to with a catalyst consisting of a molecular sieve having an effective pore size of about 8 A., said molecular sieve having been activated prior to said contacting by heating at a temperature of at least characterized in that said butene-Z is predominately in the cis form.

2. The process according to claim 1 wherein the activation is at a temperature in the range of 320 500C.

3. The process according to claim 2 wherein the activation is carried out in a non-reactive gas of air,

nitrogen, helium, argon or mixtures thereof.

4. The process according to claim 3 wherein the contacting is carried out at a temperature'in the range of 50 to C.

5. The process according to claim 4 wherein the pressure is sufficient to maintain the butene-l in liquid phase.

6. The process according to claim 5 wherein the pressure is in the range of over 1 to 50 atmospheres.

7, The process according to claim 1 wherein the molecular sieve is type X.

8. The process according to claim 7 wherein the feed comprises 40 to 60 mole percent butene-l, 6 to 10 mole percent n-butane, 0 to 4 mole percent isobutylene and 30 to 50 mole percent butene-2.

9. The process according to claim 1 wherein the process is cyclic comprising alternating regenerating and contacting cycles, provided that the regenerating cycle is carried out at a temperature of at least 400C. up to the temperature at which the molecular sieve is deactivated.

10. The process according to claim 9 wherein the regeneration temperature is in the range of 400 to 600C. 

2. The process according to claim 1 wherein the activation is at a temperature in the range of 320* - 500*C.
 3. The process according to claim 2 wherein the activation is carried out in a non-reactive gas of air, nitrogen, helium, argon or mixtures thereof.
 4. The process according to claim 3 wherein the contacting is carried out at a temperature in the range of 50* to 150*C.
 5. The process according to claim 4 wherein the pressure is sufficient to maintain the butene-1 in liquid phase.
 6. The process according to claim 5 wherein the pressure is in the range of over 1 to 50 atmospheres.
 7. The process according to claim 1 wherein the molecular sieve is type X.
 8. The process according to claim 7 wherein the feed comprises 40 to 60 mole percent butene-1, 6 to 10 mole percent n-butane, 0 to 4 mole percent isobutylene and 30 to 50 mole percent butene-2.
 9. The process according to claim 1 wherein the process is cyclic comprising alternating regenerating and contacting cycles, provided that the regenerating cycle is carried out at a temperature of at least 400*C. up to the temperature at which the molecular sieve is deactivated.
 10. The process according to claim 9 wherein the regeneration temperature is in the range of 400* to 600*C. 